Prevalence of Eimeria spp. with associated risk factors in dairy calves in Sylhet, Bangladesh

Abstract Background Bovine eimeriosis is thought to be very important for the productivity and health of cattle all over the world. Despite the importance of cattle farming in Sylhet, little is known about the prevalence of bovine Eimeria spp. and the risk factors connected with it. Objectives We conducted a study to evaluate the prevalence, species diversity and associated risk factors of Eimeria spp. in a population of 50 cattle farms from 12 upazilas (sub‐district) in Sylhet district. Methods Faecal samples were collected randomly from a total of 554 calves ranging in age from 1 month to 2 years old during a period of 7 months. We used Flotation and McMaster techniques for parasitological examination. Species identification was done by using their morphological and morphometric characteristics. Results Out of 554 calves, 308 were found to be positive for Eimeria species (55.60%). Seven species of Eimeria were identified. Among the identified species, E. bovis (38.98%), E. zuernii (26.17%) and E. alabamensis (22.38%) were found to be the most prevalent species. Mixed and species‐specific Eimeria infection were (24.73%; 95% CI 21.32–28.49) and (30.87%; 95% CI 27.17–34.84), respectively. In addition, the highest prevalence was observed at Zakigonj (68%; 95% CI 58.34–76.33) and the lowest at Companygonj (40%; 95% CI 30.94–49.80). Eimeria species intensity ranged between 50 and 76,550 oocyst per gram of faeces. Analysis of associated risk factors by using multivariate logistic regression analysis revealed that age, gender and body condition were significantly (p < 0.05) associated with Eimeria infection. Conclusions Based on these present findings, it can be assumed that ‘coccidia belong to the most prevalent pathogens in the population of calves in the study area’. Thus, the findings of this study could be used as tools for adoptive surveillance and effective control and prevention of the disease in cattle populations in this region.


INTRODUCTION
Protozoan diseases are a limitation for the advancement of dairy farming globally, especially in developing nations (Farooq et al., 2012;Om et al., 2010). Bovine coccidiosis is an important protozoan infection all over the world caused by species of the genus Eimeria in cattle, and it causes significant economic losses every year for the meat and farm businesses (Daugschies & Najdrowski, 2005). It exerts enormous economic losses to livestock industries through decreasing productivity such as reduced appetite, weight loss, reduction in growth rate, a dull appearance, and also, morbidity, mortality, the expense of treatment, and control measures (Nalbantoglu et al., 2008 bukidnonensis, E. illinoisensis, and E. brasilensis (Das et al., 2015;Dong et al., 2012;Kim et al., 2018). Generally, the most pervasive species are E. bovis, E. zuernii, E. ellipsoidalis, and E. auburnensis (Das et al., 2015;Dong et al., 2012).
Coccidiosis is an intestinal disease that affects all ages of cattle; however, clinical coccidiosis is most common in young animals, especially calves. It mainly occurs particularly because immunity is not well developed at a young age. It is frequently observed under conditions of intensive feeding and management systems (Rehman et al., 2011). Calf coccidiosis usually occurs as a subclinical disease with no apparent signs of infection. It involves great financial losses attributable to decreased appetite, weight loss, feed conversion rates, unthriftiness, diarrhoea, dysentery, anaemia, and increased susceptibility to other diseases (Bohrmann, 1991;Daugschies & Najdrowski, 2005).
The prevalence of Eimeria in cattle and buffaloes has been well reported from across the world (Dong et al., 2012;Khan et al., 2013;Laha et al., 2013), including Bangladesh (Samad et al., 2004), but information regarding the prevalence of calf coccidiosis in Bangladesh is very scarce. One study on calf morbidity and mortality in Bangladesh reported a prevalence of 27% for calf coccidiosis (Samad et al., 2001).
Despite its known effect on calf morbidity and mortality, no epidemiological study has focused on calf coccidiosis in Bangladesh.

Reference and study population
Calves from household and commercial farms in the Sylhet district of Bangladesh were the reference population. A list of the farms was collected from the local Upazila Livestock Offices as a sampling frame; five farms from each upazila were selected from this list using simple random sampling methods. Farms (N = 50) having at least 5 calves ≤ 2 years old, were selected to be sampled in this study. Therefore, a total of 554 calves were sampled, as per set criteria as follows: if there were 5-10 calves/farm, then all were sampled. If there were >10 calves, then 10 calves were selected by simple random.

Collection of faecal samples
Total 554

Data collection
The individual animal information and farm-level information were collected from the farmer's record books and the face-to-face interview of the farmers of the selected farms using a well-designed pretested questionnaire. The geographical information of each of these selected farms was captured as a geographical coordinate by Global Positioning (GPS) Reader (see Figure 1 for exact locations).

Examination of faecal sample
All collected samples were examined qualitatively, and quantitatively with routine copro parasitological techniques. Flotation method with saturated NaCl was used to identify the presence of Eimeria oocysts.
The procedure was adopted as described by (Zajac & Conboy, 2012). A slightly modified form of the McMaster technique described by Soulsby Identification of Eimeria species was based on the morphological features of the oocysts such as size, shape, colour, presence or absence of micropyle, polar cap, and so on, with the aid of taxonomic keys (Rehman et al., 2011;Soulsby, 1968). The size of the oocysts was measured by using an ocular micrometre.

Statistical analysis
Prevalence was calculated as the proportion of positive calves among the sampled individuals. The precision of this estimate was ensured by calculating the 95% confidence interval of the proportion. Association between the prevalence of coccidiosis and different intrinsic/extrinsic factors was evaluated by chi square (χ 2 test). Independent associations between the various factors and coccidiosis were assessed using logistic analysis with a backward elimination process. A p-value < 0.05 was considered statistically significant. Statistical Analysis System (SAS) version 9.4 was used to perform all statistical analyses.

Disease mapping
Geo-spatial data (latitude and longitude coordinates of selected farms) along with farm ID were collected for each study site, and then entered and stored in a Microsoft Excel spreadsheet. Prevalence maps of overall and species-specific (single) infection of calf coccidiosis were constructed in ArcMap 10.1 and ArCatalog 10.1.

RESULTS
The overall prevalence of calf coccidiosis in Sylhet was ( butions of the prevalence of overall and species-specific Eimeria infection in Sylhet district were presented in Figure 1.

DISCUSSION
Epidemiological evidence on diseases is essential for disease management and an adoptive control programme (Bonneux & van Damme, 2011). Calf coccidiosis is considered an endemic disease worldwide, and its existence has been reported in Bangladesh (Nath et al., 2013;Samad et al., 2004). However, information on epidemiological indices such as prevalence and determinants of this disease based on field observations was minimal. Thus, field-based epidemiological research on calf coccidiosis is deemed necessary to assess the magnitude and to explore the epidemiology of this disease.
This study confirms a high overall prevalence (55.60%) of calf coccidiosis at Sylhet District in Bangladesh. This outcome was not an unexpected result as calf coccidiosis is considered one of the most prevailing and frequently occurring parasitic diseases in young calves (Wood et al., 2013). This prevalence is higher than the prevalence reported in two earlier studies at Mymensingh and Chittagong (Nath et al., 2013;Samad et al., 2001). Geo-ecological differences along with the difference in study design could explain the differences in prevalence estimates of this study with these two earlier studies. Sylhet is a district with high rainfall and most cattle in this area are raised in a traditional semi  (Figure 2). Farkas et al. (2007) identified the same seven species of Eimeria from calves in Hungary.
However, Gupta et al. (2016) from Punjab, India, Koutny et al. (2012) from Austria, Heidari et al. (2014)   Prevalence maps presented in Figure 1(a) indicate that calf coccidiosis is present in all upazilas of Sylhet district with varying prevalence.
The highest prevalence of coccidiosis in general and prevalence of E.
bovis in particular was observed in Zakiganj upazila. On the other hand, Balagonj had the highest prevalence of E. Zuernii, and at Golapgonj upazila, prevalence of E. alabamensis was the highest. Importance of the infection was not investigated. For this, clinical and/or economic data would have to be collected and analysed. was identified that younger calves and females were more likely to be infected than young cattle and male, respectively. The present status of coccidiosis in calves is alarming for cattle farming in the study area.

CONCLUSIONS
Further epidemiological investigation on coccidian species, other ecological and environmental factors and economic analysis of the effect of the disease is needed to explore the complete epidemiology and ecology of calf coccidiosis.